For several months, panicked investors have been pulling cash from muni-bond funds. For investors of means, that presents an opportunity to lock in high tax-free yields for a decade or more.

Since mid-November, panicked sellers have yanked about $26 billion from muni-bond funds, disrupting a usually orderly market. For investors of means, that presents an opportunity to lock in high tax-free yields for a decade or more.

Doing so, however, takes more care than buying a muni exchange-traded fund or closed-end fund.